OBJECTIVES: The Epidemiological Study of Cardiovascular Disease developed in Evans County from the following clinical observations - 1) The prevalence rates for hypertension were twice as great in Blacks, 2) There appeared to be no black sex differential for coronary mortality as had been so well documented in Whites, 3) Blacks consumed a higher animal fat diet than Whites, 4) yet, paradoxically at the same time coronary heart disease appeared to occur much less frequently among Blacks than Whites. The study was, therefore, basically designed to answer two questions: First, WERE THESE CLINICAL OBSERVATIONS VALID? and second, IF THEY WERE VALID, WHY? It was hoped a better insight into the nature of these two disease processes could be found from studying two populations living simultaneously in the same envronment, yet each developing different disease patterns.